The present research is based on the proposition that specializations have evolved in both the structure of vocal signals and in the structure of perceptual systems that act to promote acoustic communication under the adverse conditions found in nature. In nature communicative signals may be embedded in background noises, and are subjected to degradation by wind and thermal drafts, and by the processes of absorption, diffraction and reflection. Communication is consequently constrained by the acoustics of the habitat. The acoustic ecologies of blue monkeys (Cercopithecus mitis), grey cheeked mangabeys (Cercocebus albigena) and vervet monkeys (C. aethiops) are under analysis. In addition, psychophysical experiments are being conducted to assess the relative audibility of various vocal signals in noisy habitats.